1. Field of the Invention
The present invention relates to a stepping motor, and particularly, to a connection structure of a stator yoke and a front plate.
2. Description of the Related Art
In a related-art stepping motor, as shown in FIG. 9, an attachment plate 104 which rotationally supports a rotor 103 is caulking-fixed to a motor frame 102 which holds a stator 101. Specifically, a caulking piece 106 is engaged to a caulking recess portion 105 formed by cutting at an open edge portion of the motor frame 102, and the caulking piece 106 is then caulked to fix the attachment plate 104.
However, this fixing operation of the attachment plate 104 by caulking is not easy. In addition, the caulking fixing of the attachment plate 104 causes deformation or distortion in the attachment plate 104, which in turn causes a core deviation between the rotor 103 and a bearing 107 mounted to the attachment plate 104. As a result, the rotor 103 cannot be smoothly rotated, thereby causing vibration and noise of the motor. Further, non-uniformity in properties of the motor may be caused.
In contrast to the fixing structure of the attachment plate by caulking, it is suggested that components are connected with a band without caulking-fixing (for example, see JP-A-UM-S49-46003 and JP-A-UM-S61-22473).
FIG. 10 shows a small gear fixture for a motor disclosed in JP-A-UM-S49-46003 in which a motor 206 and a gear mechanism 207 are connected by a connection frame 201. The connection frame 201 is formed by bending a metal plate into a U-shape and a tip end of a bent portion 202 is formed with an engagement edge 203 having a tip end which is slightly bent inwardly. The connection frame 201 is mounted from a side of the motor 206 and the gear mechanism 207 which are assembled each other, and the engagement edge 203 is engaged at a proper position of the gear mechanism 207, so that the motor 206 and the gear mechanism 207 are connected.
FIG. 11 shows a small synchronous motor of a band fixing type disclosed in JP-A-UM-S61-22473 in which stator cases 303, 303′ and a flange 302 are connected by a band 311. The band 311 is made of an elastic plate and has tip ends that are inwardly bent to form hook-shaped bent portions 312. The hook-shaped bent portions 312 are pressed in recess holes 313 of the flange 302 to latch the band 311, thereby connecting the stator cases 303, 303′ and the flange 302.
However, according to the connection frame 201 disclosed in JP-A-UM-S49-46003, the engagement edge 203 provided at the tip end of the bent portion 202 of the connection frame 201 is formed by simple bending, and therefore, it cannot be said that the engagement is surely sufficient. In addition, the motor 206 may be moved in a peripheral direction while the connection frame 201 being mounted. Thus, it cannot be said that the rotation is surely prevented.
According to the band 311 disclosed in JP-A-UM-S61-22473, the tip ends thereof are inwardly bent to form the hook-shaped bent portions 312, which are pressed in the recess holes 313 of the flange 302. Thus, the engagement feature is not problematic. However, since an extruded part formed at a back end of the band 311 is simply fitted in an inner hole of the stator case 303′, there is a concern that the flange 302 may be rotated together with the band 311 depending on a degree of the fitting of the extruded part. That is, it cannot be said that the rotation is surely prevented. In addition, according to JP-A-UM-S61-22473, corner parts of both ends of the band 311 are protruded, so that a space for accommodating the corner parts is required. Thus, it is difficult to realize reducing the size.